This invention relates to an ink jet recording head using a piezoelectric thin film for an ink jet drive source and a manufacturing method therefor. Further, it relates to an ink jet recorder using the recording head.
There is a piezoelectric ink jet recording head using PZT elements comprising PZT of piezoelectric elements as electromechanical transducer elements of liquid or ink jet drive source. This type of the piezoelectric ink jet recording head is proposed in, for example, Japanese Patent Application Laid-Open No. Hei 5-286131.
This conventional head will be discussed with reference to FIG. 10. The recording head has separate ink passages (ink pressure chambers) 9 on a head base 1 and a diaphragm 8 so as to cover the separate ink passages 9. A common electrode (lower electrode) 3 is formed so that it is attached to the diaphragm 8, and PZT elements 4 are placed so as to reach the tops of the separate ink passages 9, a separate electrode (upper electrode) 5 being placed on one face of the PZT element.
In the recording head, an electric field is applied to the PZT element for displacing the same, thereby pushing out ink in the separate ink passage from a nozzle of the separate ink passage.
The sequence of events for the inventor to diligently study conventional ink jet recording heads and reach the invention will be discussed.
In the conventional ink jet recording head previously described, a pattern shift occurs between the PZT element and the upper electrode and even if they are patterned with the same pattern, it is feared that a leak between the upper electrode and the common electrode will occur due to a pattern shift between the PZT element and the upper electrode.
Then, to attempt to avoid this problem, it becomes necessary to make the upper electrode pattern smaller than the PZT element pattern. That is, the form shown in FIG. 10 is changed to that in FIG. 11. In doing so, it is feared that the electric field on the upper electrode 5 side will not be applied to the piezoelectric part where the upper electrode does not exist, worsening the efficiency for jetting ink.
That is, the part of the piezoelectric body, to which no electric field is applied, not deformed restrains the deformed part, lessening displacement of the entire piezoelectric body. If the upper electrode is not positioned at the width direction center of the piezoelectric film, namely, the widths of the undeformed parts of the piezoelectric film at the left ΔX1 and right ΔX2 shown in the FIG. 43 differ (ΔX1>ΔX2, for instance), the piezoelectric film deformation becomes distorted, lowering the jet characteristic and stability. The same reference numbers in FIGS. 10, 11 and 43 are used to designate the same elements.
Then, to solve the problem, the inventor forms the piezoelectric body as a thin film and etches the piezoelectric thin film and separate electrodes at the same time, for example, by using a photolithography technique, thereby providing a new ink jet recording head with the piezoelectric thin film and electrodes patterned in the same shape.
On the other hand, to jet ink equal to or more than ink with an ink jet using a bulk piezoelectric body for piezoelectric thin film of thin PZT element, it is desirable to form a PZT thin film having an extremely large piezoelectric constant more than bulk PZT for deforming a diaphragm.
Generally, the piezoelectric constant of the PZT thin film is only a half to a third of the piezoelectric constant of bulk PZT and if only PZT elements differ and other design values are the same, it is difficult to use the PZT thin film to jet ink more than ink with bulk PZT.
A method of increasing the PZT thin film formation area is available to enable use of a PZT thin film having a small piezoelectric constant. According to this method, an amount of ink required for printing can be jetted, but if the PZT thin film area increases, ink jet recording head cannot be formed in high density and high-definition print quality cannot be provided.